Gaseous discharge high intensity lamp with fluid cooled electrode

ABSTRACT

A high intensity light source is provided by an arc discharge xenon lamp which includes an anode and a cathode electrode enclosed within a sealed, gas-filled, light transparent envelope. The electrodes are disposed in spaced relation such that an arc may be energized across the adjacent ends when a voltage is applied thereacross. The anode electrode is hollow and closed at the arc end. The internal surface at the hollow end has at least one protrusion to increase the exposure surface and a fluid coolant provides greater heat dissipation therefrom. Preferably the anode electrode includes a tubular member of one metal having an enclosed end, a layer of tungsten capping the external arc end to form the arcing surface, and a further metallic layer joining the tubular member and the tungsten layer. In one embodiment, the metallic layer has a thermal expansion coefficient of an intermediate value between that of the tungsten layer and tubular member.

[ 1 Mar. 27, 1973 envelope. The electrodes are 8 Claims, 4 Drawing Figures A high intensity light source is provided by an arc discharge xenon lamp which includes an anode and a cathode electrode enclosed within a sealed, gas-filled,

disposed in spaced relation such that an arc may be energized across the adjacent ends when a voltage is applied thereacross. The anode electrode is hollow and closed at the arc end. The internal surface at the hollow end has at least one protrusion to increase the exposure surface and a fluid coolant provides greater heat dissipation therefrom. Preferably the anode electrode includes a tubular member of one metal having an enclosed end, a layer of tungsten capping the external arc end to form the arcing surface, and a further metallic layer joining the tubular member and the d m n u a a E g r L m H M 0 m G w d I m 1 a m w A S t R m u T e S R Th m d 8 n m I O8 0 C km .w I Y MN 6 m B0 0 n 7 n .e 5 A MM Paul W. Hemminger, Charles L. Johnson, Jr., Philip light transparent tungsten layer. In one embodiment, the metallic layer has a thermal expansion coefficient of an intermediate value between that of the tungsten layer and tubular United States Patent Beese et al.

154] GASEOUS DISCHARGE HIGH INTENSITY LAMP WITH FLUID COOLED ELECTRODE [75] lnventors: Norman C. Beese, Verona, NJ

James J. Malloy, Jr., Easton, Pa.

[73] Assignee: International Telephone and Telegraph Corporation, Nutley, NJ.

Apr. 22, 1970 [21] Appl. No.: 30,716

221 Filed:

[51] Int. 61/06, HOlj 61/52 References Cited Sileo....... 9/1970 Paquette 10/1968 Strupczewski.....

UNITED STATES PATENTS Primary Examiner-Roy Lake Assistant Examiner-Palmer C. Demeo GASEOUS DISCHARGE HIGH INTENSITY LAMP WITH FLUID COOLED ELECTRODE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high intensity light sources and, more particularly, to a gaseous are discharge lamp of improved efficiency.

2. Description of the Prior Art High intensity light sources of previously known gaseous arc discharge types, such as the xenon short arc lamp shown in US. Pat. No. 3,311,769, issued on Mar. 28, 1967, include internally cooled anode and cathode electrodes enclosed within a sealed, gas-filled, light transparent envelope made of quartz glass. The ends of the two electrodes are disposed in spaced relation such that an arc may be energized when a voltage is applied thereacross. To cool the electrodes, a fluid coolant is applied internally to hollow regions within the electrodes. The electrodes are made of a molybdenum tube with a tungsten cap welded thereto to form the arcing end. The internal surface at the arc end of the hollow region is rounded to permit laminar flow of the coolant.

While the aforedescribed xenon short are lamp is satisfactory in certain applications, there is an ever increasing demand for still higher intensity light sources in military, civilian and space activities for use as searchlights, floodlights, and solar simulator radiation sources that require relatively long effective life and that are efficient and reliable.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide improved high intensity light sources of the gaseous arc lamp type.

It is another object of the present invention to improve the cooling efficiency of internally cooled electrodes of high intensity xenon arc lamps and provide increased life and reliability.

These and other objects of the present invention are achieved in accordance with a preferred embodiment of the present invention by providing at least one protrusion on the internal surface of the hollowed electrode end to increase the surface area exposed to and coming in contact with the coolant and by providing an internal surface of copper at a portion of the hollowed electrode. The increased exposure surface increases the cooling rate of the electrode while the copper surface provides an improved thermal conduction path from the heated gas within the enclosed envelope to the coolant within the hollow electrode.

It is a feature of the present invention that the body of the anode electrode includes at least a portion of copper for better thermal conduction, rather than being made only of molybdenum, as used in the prior art.

It is another feature of the present invention that a metallic layer of a given metal joins the tubular body of a different metal with the tungsten arc end to minimize the adverse effects of a large difference in the thermal expansion coefficient between the two, one of the metals having a thermal expansion coefficient of an intermediate value between that of tungsten and the other metal.

It is another feature of the present invention to have an electrode coated with a black material such as platinum black or copper oxide so that the electrode can absorb heat from the gaseous discharge at a faster rate to increase the thermal conduction of the heat to the coolant.

The aforementioned objects and features of the present invention may be more fully comprehended from the following description of the preferred embodiment in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional view showing a portion of a known type of gaseous short are lamp structure along a longitudinal axis;

FIG. 2 is a cross-sectional view of the anode electrode structure with a protruding internal cooling surface in accordance with the present invention;

FIG. 3 is a cross-sectional view of another embodiment of an electrode structure having fin-like protrusions from the internal cooling surface; and

FIG. 4 is a cross-sectional view along AA of FIG. 3 showing a spiral form of the tin-like protrusion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a portion of a known type of gas-filled short are lamp structure. The lamp structure typically comprises a sealed quartz glass envelope ll filled with a rare gas such as xenon. The envelope encloses an anode electrode 12 and a cathode electrode 13. The anode electrode 12 is made of a molybdenum tube 15 with a closed end onto which is brazed a tungsten cap 16 forming the arcing surface of the anode electrode. The electrodes 12 and 13 are disposed in an axial alignment in a predetermined spaced relationship so that when selected voltages are applied thereacross, an arc is energized across the gap 18 and emits a high intensity light. The electrodes are securely held within the quartz glass envelope 11 by a suitable electrode support means 19. Typically, the anode electrode 12 has a tip of a different configuration than that of the cathode electrode 13 although the present invention is not limited to electrodes having any predetermined tip configurations. Each of the electrodes have hollow end portions to receive a coolant, such as water, for cooling the electrodes when heated by the energizing arc discharge current. The anode electrode has a closed end into which a coolant is pumped through a supply tube 20 disposed within the hollowed region of the electrode. The coolant flows over the are rounded inner end surface and out through the passageways between the interior surface of the electrode 12 and the tube 20.

FIG. 2 shows the anode electrode in accordance with the present invention wherein parts designated as 15, 16 and 20 correspond respectively to those in FIG. 1. As shown, the internal surface of the electrode is lined with a layer 24 of copper having at least one protrusion 25 on the internal surface of the arc end. Use of the copper lining improves the thermal conduction of the heat from the tungsten cap 16 to the coolant and provides a high heat gradient so that the temperature of the electrode surface coming in contact with the coolant is kept at a level substantially below that of the tungsten. The protruding surface further enhances the cooling speed of the electrodes by providing an increased surface exposed to and coming in contact with the coolant.

To assure a constant thermal conductivity throughout the life of the lamp, the tungsten cap 16 is preferably arc welded along the end surface 23 of a high density molybdenum tube in an atmosphere of helium or argon gas. This eliminates the need for a platinum flux employed in the prior art to provide thermal and electrical conductivity between the tungsten cap 16 and molybdenum tube 15. The internal surface of the tungsten cap 16 and the end portion of the molybdenum contiguous therewith are lined with a layer of OFHC copper 24 melted in a vacuum or in a reducing atmosphere. OFHC is an acronym for high purity oxygen free high conductivity copper which is particularly useful within an electron tube as there is a minimum of trapped gases that can be released during operation of the tube. The copper layer 24 is then machined to have a protruding surface 25. Advantageously as shown, the protruding surface 25 may be in a form carved out by a concave surface of a tool transversely rotated about an axis at one of its ends.

The tungsten cap and molybdenum surfaces are electrolytically cleaned and electroplated with a thin layer of copper before the copper lining 24 is applied, to assure good adherence and a bond of high thermal conductivity. An anode for a kw xenon arc water cooled lamp was constructed with an outer diameter of about 31mm and a length of about 380 mm and included a copper lining of a thickness between 1 to 3 mm at the sides, 3 to 6 mm over most of the rest of the layer, and 10 to 12 mm at the center across the protrusion. The peripheral end surface 26 of the supply tube 20 facing the copper lining 24 was contoured to conformsubstantially to the concave surfaces of the copper lining 24 around the protrusion and was provided with a nozzle exit 22 to increase the speed of the coolant entering onto the protruding surface. The passageways between the electrode and the supply tube were dimensioned to provide a relatively uniform spacing so that the water used as the coolant could flow in a smooth laminar fashion and substantially at a constant speed. The increased exposure surface and the constant rate of flow of the water eliminate formation of local hot points which tended to form in the priorly known electrodes and which shortened the life of the xenon lamp.

FIGS. 3 and 4 show another embodiment of the present invention. In this instance, the internal surface of the anode electrode has protrusions in a form of a plurality of spiral fins 31 and 32 extending from the internal surface of the arcing end facing the hollow region. The anode electrode 15 is made of copper instead of molybdenum. As shown, the arc end 33 of the copper electrode 15 is formed of the same copper as that of the electrode body. Since copper is a better thermal conductor, it increases the rate at which heat can be conducted to the coolant from the hot energized gas. The projecting spiral fins are formed by carving corresponding intermediate channels 34, 35 into the end of the copper tube substantially in parallel with the longitudinal axis. The bottom of the channels at the arc end are rounded to help the coolant flow in a laminar fashion on'the surfacesl Preferably the fins are made to taper off in thickness toward the longitudinal axis in such a manner that the widths of the channels formed thereby are wider at the center and narrow at the outer periphery. The shape of the fins permit the coolant to flow therethrough at constant velocity and with a laminar flow toward the periphery of the tubular member. Each of the fins 31, 32 are spaced some distance away from the longitudinal axis of the tube to form an opening 36 where the coolant can enter. The coolant supply tube 37 is provided with a nozzle exit 38 substantially in alignment with the longitudinal axis of the electrode and the opening 36 so that the coolant enters at the center of the fins. The end of the coolant supply tube 37 fits closely against the end of tube 33 to seal off the channels formed by the fins except at the outer periphery along the side of the tube to provide exit paths 39 for the coolant. Thus, the coolant entering the central space 36 flows through the channels 34, 35

and then through the passageways 39 between the supply tube 37 and the internal surface of the electrode The tubular member 15 is made of copper in place of the molybdenum previously used, to permit heat conduction from the energized gas at a faster rate. The are end 33 of the tubular member 15 is capped with a layer of forged high density tungsten 40. To minimize adverse effects of the wide difference in the thermal expansion coefficient between the copper and tungsten, an intermediate layer 41 of a metallic material having a thermal expansion coefficient between that of copper and tungsten is provided. Such intermediate layer is particularly important in lessening the tendency for cracks to develop at the center of the anode focal spot during the period of high arcing currents. For the intermediate layer, molybdenum is suitable. The molybdenum layer is brazed to the tungsten cap with platinum flux and to the copper body in an atmosphere of hydrogen or argon gas. A granular layer of crushed tungsten has also been found satisfactory for the intermediary layer, in which case, the outer end of copper electrode 33 is fused to tungsten cap 40 through the interstices between the grains of the crushed tungsten layer. In accordance with the afore-described principles, a novel anode electrode was constructed for a 20 kw xenon arc lamp which included two protruding fins, each being about 2 mm thick and about 7 mm deep at the center along the longitudinal axis of the electrode. The channels formed between the fins were about 3 mm wide at the center and gradually tapered to about 1.5 mm at the terminations along the sides of the electrode. The supply tube 37 had a nozzle hole 38 about 6.5 mm in diameter and the end 45 of the supply tube 37 was in direct contact with the end surface of the fins 31 and 32. The outer diameter of the supply tube 37 was spaced about 1.0 mm from the inner diameter of the electrode 15 to provide a path for the coolant. Four pins 42 were used to space the supply tube 37 at the proper location relative to the electrode 15. To improve heat absorption capacity of the electrode, the surface of the copper electrode 15 was coated with an external layer 43 of black material such as a platinum black or copper oxide.

The embodiments described above are merely illustrations of the present invention. Various modifications may be made without departing from the spirit and scope of the present invention.

What is claimed is:

l. A high intensity light source comprising:

a sealed, gas-filled envelope having a light transparent portion;

a first and a second electrode disposed in said envelope with an end of each in spaced relation such that an arc may be energized across the adjacent ends thereof upon application of a selected voltage thereacross, said first electrode being an anode including a hollow tubular member of one metal disposed in the region of the arc end and having said end closed, the internal surface of said closed end having at least one protrusion increasing the exposure surface thereof and heat dissipation therefrom, said protrusion including a spiral fin having channels between adjacent walls of said fin, said closed end having an external layer of tungsten and an underlying layer adjoining said tubular member and said tungsten layer; and

means for applying coolant to said internal surface of said first electrode including an inner tube within said hollowed electrode and a passageway for said coolant between said inner tube and closed end, the exit end of said inner tube including a nozzle having a constricted opening centrally positioned over said fin such that the coolant enters substantially at the center of said fin and flows radially outwardly through said channels and exits through said passageway.

2. A high intensity light source in accordance with claim 1, wherein said tubular member is copper and includes said internal closed end surface and protrusion thereon.

3. A high intensity light source in accordance with claim 2, wherein said intermediate metallic layer is interposed between said tungsten layer and said copper member, said metallic layer being of a material having a thermal expansion coefficient of an intermediate value between that of said tungsten cap and said copper member, and being fused to said copper member and said tungsten layer.

4. A high intensity light source in accordance with claim 2, wherein said exit end and nozzle are in contact with the protruding end of said fin.

5. A high intensity light source in accordance with claim 4, wherein said intermediate metallic layer is of molybdenum fused to said tungsten layer and to said copper member.

6. A high intensity light source in accordance with claim 4, wherein said metallic layer is a granular layer of crushed tungsten and wherein the arc end of said copper member is fused onto said tungsten layer through the interstices between the grains of said crushed tungsten.

7. A high intensity light source in accordance with claim 4, wherein said copper member includes an external coating of a black metallic material for increas ing heat absorption.

8. A high intensity light source in accordance with claim 7, wherein said black material is selected from the group consisting of platinum black and copper oxide. 

1. A high intensity light source comprising: a sealed, gas-filled envelope having a light transparent portion; a first and a second electrode disposed in said envelope with an end of each in spaced relation such that an arc may be energized across the adjacent ends thereof upon application of a selected voltage thereacross, said first electrode being an anode including a hollow tubular member of one metal disposed in the region of the arc end and having said end closed, the internal surface of said closed end having at least one protrusion increasing the exposure surface thereof and heat dissipation therefrom, said protrusion including a spiral fin having channels between adjacent walls of said fin, said closed end having an external layer of tungsten and an underlying layer adjoining said tubular member and said tungsten layer; and means for applying coolant to said internal surface of said first electrode including an inner tube within said hollowed electrode and a passageway for said coolant between said inner tube and closed end, the exit end of said inner tube including a nOzzle having a constricted opening centrally positioned over said fin such that the coolant enters substantially at the center of said fin and flows radially outwardly through said channels and exits through said passageway.
 2. A high intensity light source in accordance with claim 1, wherein said tubular member is copper and includes said internal closed end surface and protrusion thereon.
 3. A high intensity light source in accordance with claim 2, wherein said intermediate metallic layer is interposed between said tungsten layer and said copper member, said metallic layer being of a material having a thermal expansion coefficient of an intermediate value between that of said tungsten cap and said copper member, and being fused to said copper member and said tungsten layer.
 4. A high intensity light source in accordance with claim 2, wherein said exit end and nozzle are in contact with the protruding end of said fin.
 5. A high intensity light source in accordance with claim 4, wherein said intermediate metallic layer is of molybdenum fused to said tungsten layer and to said copper member.
 6. A high intensity light source in accordance with claim 4, wherein said metallic layer is a granular layer of crushed tungsten and wherein the arc end of said copper member is fused onto said tungsten layer through the interstices between the grains of said crushed tungsten.
 7. A high intensity light source in accordance with claim 4, wherein said copper member includes an external coating of a black metallic material for increasing heat absorption.
 8. A high intensity light source in accordance with claim 7, wherein said black material is selected from the group consisting of platinum black and copper oxide. 